import java.awt.*;
import java.util.*;
import java.text.*;

public class ClockComp extends Component {
    // Using a variation on the "Self-Running Object"
    // technique from Chapter 11 of "Java Thread Programming".
    // See that chapter of the book for more on internal threads

    private volatile String timeStr;
    private volatile boolean noStopRequested;
    private Thread internalThread;
    private DateFormat df;
    private Dimension prefSize;
    private Font font;

    public ClockComp() {
        prefSize = new Dimension(200, 40);
        font = new Font("Monospaced", Font.BOLD, 14);

        df = DateFormat.getTimeInstance(DateFormat.LONG);
        updateTime();
    }

    public Dimension getPreferredSize() {
        return prefSize;
    }

    public void paint(Graphics g) {
        g.setFont(font);
        g.setColor(Color.blue);
        g.drawString(timeStr, 0, 20);
    }

    private void updateTime() {
        timeStr = df.format(
                new Date(System.currentTimeMillis()));
    }

    private void runWork() {
        try {
            while ( noStopRequested ) {
                updateTime();
                repaint();
                Thread.sleep(300);
            }

            timeStr = "STOPPED - by flag";
        } catch ( InterruptedException x ) {
            timeStr = "STOPPED - by InterruptedException";
        } finally {
            repaint();
            System.out.println("clock is stopped");
        }
    }

    public synchronized void start() {
        if ( ( internalThread != null ) && 
             ( internalThread.isAlive() == true )
           ) {

            // running already, ignore
            System.out.println(
                "clock is already running --ignoring start");
            return;
        }

        noStopRequested = true;
        Runnable r = new Runnable() {
                public void run() {
                    runWork();
                }
            };

        internalThread = new Thread(r, "clock");
        internalThread.start();
        System.out.println("clock started");
    }

    public synchronized void interruptOnly() {
        if ( ( internalThread != null ) && 
             ( internalThread.isAlive() == true )
           ) {
            internalThread.interrupt();
            System.out.println(
                    "clock received interrupt only");
        }
    }

    public synchronized void stopRequest() {
        if ( noStopRequested ) {
            noStopRequested = false;
            internalThread.interrupt();
            System.out.println(
                    "clock received stop request");
        }
    }
}